1. Field of the Invention
The present invention relates generally to power transmission devices and more particularly to V-belt drive mechanisms of the type wherein a V-belt pulley is adjustable to change its effective diameter.
2. Description of the Prior Art
V-belt drives are widely used in machinery and power driven equipment of many types, including lawn care equipment. A typical use, for example, would be to transmit power to the drive wheels for propelling a mower along the ground. In certain situations, it may be desirable to provide a choice of several speeds for such equipment, but without the weight and expense of a gear box. A variable pitch V-belt pulley or pulleys can provide the desired adjustment.
Various types of variable pitch V-belt pulleys have been previously proposed and which feature split pulley halves which were selectively adjustable by some type of mechanism on the pulley hubs. Typically, this mechanism involved a threaded male portion of one pulley half hub joined with a female threaded portion of an opposed pulley half hub. The pulley halves could be selectively rotatably positioned and fixed in the desired position by means of a screw or the like to establish the desired pitch diameter of the pulley. Examples of such arrangements are shown in U.S. Pat. Nos. 2,234,917, 4,177,685 and 4,226,133. A variation on this basic design is shown in U.S. Pat. No. 2,555,189 wherein both pulley halves are threadedly adjustable on a threaded bushing and secured at the desired spacing thereon by means of set screws engaging slots in the bushing.
A different although related arrangement for varying the spacing of a variable pitch V-belt pulley is shown in U.S. Pat. No. 1,756,592 wherein a diagonal slot is provided in the hub of one pulley half which is disposed in telescoping relation with the hub of the opposed pulley half which carries a bolt engaged in the diagonal slot. Relative rotation of the pulley halves with the bolt loosened permits the adjustment of the pulley to the desired pitch diameter, whereupon the bolt can be tightened to fix the pulley halves at the desired effective diameter.
Although the described prior art devices will accomplish the objective of varying the pulley pitch diameter, the structures are complex and expensive to produce. Furthermore, the prior art devices typically are larger and heavier in view of their elaborate hub structure. A further disadvantage of the typical prior art device is the need for tools to effect a change in the pulley diameter and sufficient skill and experience to provide the desired speed adjustment. Since the devices typically allow an infinite speed adjustment within certain ranges, it may be difficult to establish a particular desired pulley diameter without some trial and error.